User Manual

Table Of Contents
Brushless Motor Connections and Operation
122 Advanced Digital Motor Controller User Manual V2.0, July 8, 2019
V
U
W
V+
GND
Ut
Ub
Vt
Vb
Wt
Wb
FIGURE 8-17. Active and floating phases
The figure above shows the state of the transistor switches during one of the six commu-
tations phases. The current flows from the battery through the U winding, then through
the V winding to ground. The W winding is floating. Since no current is flowing through W,
the W terminal has the voltage potential of the BEMF that is induced in the W winding,
added to the voltage at the motor’s center point. The center point motor is exactly half the
V+ voltage, assuming that all windings have the same resistance..
ZC ZC
ZC ZC
ZC ZC ZC
0V
V+
0V
V+
0V
V+
t0 t1 t2 t3 t4 t5 t0
Vu
Vv
Vw
FIGURE 8-18. Six-phases Trapezoidal commutation, BEMF and Zero Crossing
The figure above shows the voltage at each of the windings during the 6 commutation
phases. Notice how the voltage of the floating phase ramps between 0 and V+, and be-
tween V+ and 0, as the rotor moves 60 degrees. The point in the ramp that is exactly at
half the supply voltage is called Zero Crossing. Commutation must occur 30 degrees of
rotation later. Roboteq controllers use Back EMF Integration technique in order to deter-
mine that precise moment.